The present invention relates generally to fiber optic cables and, more particularly, to fiber optic cables having at least one strength member.
Fiber optic cables include optical fibers that are capable of transmitting voice, video, and data signals. Fiber optic cables have advantages over electrical voice, video and data signal carriers, for example, increased data capacity. As businesses and households demand increased data capacity, fiber optic cables can eventually displace electrical voice, video, and data signal carriers. This demand for fiber optic cables has led to shortages of fiber optic cable materials.
Aramid fibers are cable materials that can serve several functions, such as: providing tensile strength to the fiber optic cable; cushioning the optical fibers from compression and impact loads; covering the optical fibers during the extrusion of the outer jacket to prevent the optical fibers from sticking to the extruded outer jacket; and binding the optical fibers together to prevent relative movement. Aramid fibers can, however, be expensive.
In addition to being cost effective, fiber optic cables should be simple to manufacture and have a relatively small diameter. An example of a reduced diameter indoor fiber optic cable is disclosed in U.S. Pat. No. 5,627,932, which is incorporated herein by reference. This fiber optic cable requires a tight buffered optical fiber or fibers disposed within a layer of loose aramid fibers, more specifically Kevlar(copyright) aramid fibers, which are surrounded by an outer jacket. This cable can be made of flame retardant materials for riser or plenum applications; however, the cable has disadvantages. For example, the cable requires a significant amount of aramid fibers that are typically expensive, thereby increasing cable manufacturing costs.
Fiber optic cables should also have acceptable levels of attenuation. An example of a fiber optic cable designed to prevent attenuation as a result of the manufacturing process is disclosed in U.S. Pat. No. 5,822,485, which is incorporated herein by reference. This fiber optic cable or cable element requires a jacket surrounding an optical fiber and aramid fibers, such as Kevlar(copyright), without an intended lay. The manufacturing process requires that the tension applied to the aramid fibers during manufacturing does not exceed the tension applied to the optical fiber during manufacturing. Although this fiber optic cable is designed to prevent attenuation induced during the manufacturing process, this design has several disadvantages. For example, the cable requires a significant amount of aramid fibers, which if available, are expensive and increase cable manufacturing costs.
Conventional textile glass or other fiberglass components (hereinafter conventional glass components), for example CR-785D and CR-785G, which have essentially the same glass composition with respect to each other, but different coatings, are commercially available from Owens-Corning Inc. Conventional glass components have been developed for outdoor fiber optic cables but have had limited application in premises fiber optic cables. Additionally, these conventional glass components are relatively stiff and have a lower tensile modulus when compared with aramid fibers of similar size. Another conventional glass component used in outdoor fiber optic cables is a 7065 denier yarn. This standard conventional glass component was selected based on tensile strength, more specifically, one strand of 7065 denier conventional glass was typically selected as the standard because it has the same tensile strength as one strand of a 2450 denier aramid fiber.
The present inventor has discovered that a factor limiting the use of conventional glass components in premises fiber optic cables is the incompatibility of these fiberglass components with certain optical fibers, more specifically, 50/125 xcexcm tight buffered optical fibers. The research of the present inventor has shown that 50/125 xcexcm optical fibers generally have increased bend sensitivity compared with other optical fibers, such as 62.5/125 xcexcm tight buffered optical fibers. Consequently, when conventional glass components were employed in fiber optic cables having 50/125 xcexcm tight buffered optical fibers, testing revealed unacceptably high levels of attenuation.
FIG. 1 (prior art) is a cross-sectional view of a fiber optic premises cable 10. Cable 10 comprises a plurality of 50/125 xcexcm tight buffered optical fibers 14 stranded around a central strength member 12, which can include glass reinforced plastic (GRP), plastics or aramid fibers. Interposed between optical fibers 14 and an outer jacket 18 is a required layer of aramid fibers 16, which are stranded around optical fibers 14. Outer jacket 18 surrounds and contacts layer 16. This contact results in a force between the inner surface of outer jacket 18 and the outer surface of layer 16 holding components 12, 14 and 16 in place.
Cable 10 exhibits acceptable performance characteristics when layer 16 comprises aramid fibers, which are relatively soft and flexible. However, the present invention has discovered that cable 10 exhibits unacceptable levels of attenuation and/or unacceptable performance characteristics if layer 16 comprises conventional glass components. The unacceptable characteristics are believed to be due to the fact that conventional glass components are relatively hard and stiff when compared with aramid fibers of the same size.
An aspect of the present invention includes a fiber optic cable having at least one optical fiber component and at least one strength member disposed adjacent to the at least one optical fiber component. The at least one strength member includes a yarn with a coating system having a percentage by weight, based on the dry weight of the yarn, of about 2.0% or less. A jacket generally surrounds the at least one optical fiber component and the at least one strength member. Additionally, the cable can be riser or plenum rated.
Another aspect of the present invention includes a fiber optic cable having at least one optical fiber component stranded around a central member. A plurality of strength members forming a first layer stranded around the at least one optical fiber component. The plurality of strength members includes at least one yarn with a coating system having a percentage by weight, based on the dry weight of the yarn, of about 2.0% or less. A jacket generally surrounds the at least one optical fiber component, central member and the plurality of strength members. The central member, the at least one optical fiber component and the first layer comprising a cable core having a peak pull-out force of about 1 newton or less. Additionally, the cable can be riser or plenum rated.
A further aspect of the present invention includes a fiber optic cable including at least one tight-buffered optical fiber component stranded around a central member. A plurality of strength members forming a first layer stranded around the at least one optical fiber component, the plurality of strength members includes at least one yarn. The yarn includes a coating system having a percentage by weight, based on the dry weight of the yarn, of about 2.0% or less. A space having a range of about 0.03 millimeters to about 1.0 millimeters, at the time of extrustion, is disposed between the plurality of strength members and a jacket generally surrounding the at least one optical fiber component, central member and the plurality of strength members. Additionally, the cable can be riser or plenum rated.
A still further aspect of the present invention includes a method of manufacturing a fiber optic cable. The method includes paying off at least one optical fiber component and at least one strength member. The at least one strength member includes at least one yarn. The yarn includes a coating system having a percentage by weight, based on the dry weight of the yarn, of about 2.0% or less. A cable core defined by placing the at least one strength member adjacent to the at least one optical fiber component. The method also includes extruding a jacket around the cable core. Additionally, the method of manufacture can include a tube-on extrusion process that may provide a space at the time of extrusion.
Yet another aspect of the present invention includes a fiber optic cable including at least one optical fiber component and at least one strength member disposed adjacent to the at least one optical fiber component. The at least one strength member can include a yarn. The yarn includes a coating system having a percentage by weight, based on the dry weight of the yarn, of about 2.0% or less. A jacket generally surrounds the at least one optical fiber component and the at least one strength member. The fiber optic cable includes a delta attenuation of about 0.3 dB or less over the range of about 0% fiber strain to about 1.0% fiber strain. Additionally, the jacket of the cable can be formed of a flame-retardant material.
Still another aspect of the present invention includes a fiber optic cable including at least one optical fiber component and at least one strength member disposed adjacent to said at least one optical fiber component. A jacket generally surrounds the at least one optical fiber component and the at least one strength member. The cable includes a delta attenuation of about 0.3 dB or less over the range of about 0% fiber strain to about 1.0% fiber strain. The said at least one optical fiber component and said at least one strength member comprising a cable core having a peak pull-out force of about 1 newton or less.